Transplantation of germ line stem cells for the study and manipulation of spermatogenesis

The germ cell marker dead end reveals alternatively spliced transcripts with dissimilar expression

Since the late 19th century, the Amazon species Colossoma macropomum (tambaqui) has been exploited commercially and the climate change has contributed to decline in tambaqui numbers. Although germ cell cryopreservation and transplantation can help preserve the species’ genetic resources semipermanently, its germ cell behavior has not been analyzed to date. In this study, we isolated the tambaqui’s dead end gene (dnd) homolog (tdnd) and used it as a molecular marker for germ cells to obtain basic information essential for transplantation. The amino acid sequence showed 98% similarity and 53% identity with the zebrafish dnd. Phylogenetic analysis and the presence of consensus motifs known for dnd revealed that tdnd encodes the dnd ortholog and its transcript is detectable only in the testes and ovaries, showing a strong positive signal in oocytes and spermatogonia. The tambaqui possesses, at least, three different transcripts of tdnd which show dissimilar expression profile in undifferentiated and sexually mature animals, suggesting that they play distinct roles in germline development and they may influence the choice of donors for the cell transplantation study.

Germ cell transplantation as a potential biotechnological approach to fish reproduction

Although the use of germ cell transplantation has been relatively well established in mammals, the technique has only been adapted for use in fish after entering the 2000s. During the last decade, several different approaches have been developed for germ cell transplantation in fish using recipients of various ages and life stages, such as blastula-stage embryos, newly hatched larvae and sexually mature specimens. As germ cells can develop into live organisms through maturation and fertilization processes, germ cell transplantation in fish has opened up new avenues of research in reproductive biotechnology and aquaculture. For instance, the use of xenotransplantation in fish has lead to advances in the conservation of endangered species and the production of commercially valuable fish using surrogated recipients. Further, this could also facilitate the engineering of transgenic fish. However, as is the case with mammals, knowledge regarding the basic biology and physiology of germline stem cells in fish remains incomplete, imposing a considerable limitation on the application of germ cell transplantation in fish. Furthering our understanding of germline stem cells would contribute significantly to advances regarding germ cell transplantation in fish.

Progress and prospects: techniques for site-directed mutagenesis in animal models

In the past 2 years, new gene-targeting approaches using adeno-associated virus and designer zinc-finger nucleases have been successfully applied to the production of genetically modified ferrets, pigs, mice and zebrafish. Gene targeting using these tools has been combined with somatic cell nuclear transfer and germ cell transplantation to generate gene-targeted animal models. These new technical advances, which do not require the generation of embryonic stem cell-derived chimeras, will greatly accelerate the production of non-mouse animal models for biomedical research.